This invention relates to radar systems that simultaneously transmit and/or receive a plurality of beams of high frequency energy in a scanning mode to identify the presence, locus and characteristics of scatters in a region of space.
It is a problem in the field of radar systems, and weather radar systems in particular, to implement an inexpensive system that collects sufficient data to provide accurate information to the users relating to the presence, locus and characteristics of scatters in a region of space, in a short period of time. Radar systems can be characterized in terms of the basic system architecture as either monostatic radar systems which use a single transmitter and receiver or bistatic radar network systems which use a single radar transmitter and a plurality of receivers, at least one of which is located remotely from the transmitter site.
Included in the field of monostatic radar systems are the standard narrow beam radar systems which transmit a single narrow beam of high frequency radiation, then receive signals, which constitute components of this narrow beam that have been reflected off scatterers located in the path of the beam. These systems usually include a mechanically driven antenna to execute a predetermined scan pattern that covers a predetermined volume of space. The scanning speed is limited by the ability to obtain independent meteorological samples using a single frequency and by the ability to mechanically move a large antenna, thereby preventing these systems from both scanning extremely rapidly and frequently revisiting particular regions of space. To increase the accuracy of the data produced by the narrow beam radar systems, expensive rotating high gain antennas are used. As a result, the cost of implementing, operating, and maintaining such systems is high. Furthermore, the accuracy of the data produced is adversely affected by the infrequent scan pattern of the rotating antenna. These narrow beam radar systems, when used as a weather radar, collect data that is indicative of only the radial component of the wind field present in the predetermined volume of space.
Included in the field of monostatic radar systems are the broad beam radar systems which transmit a single broad beam of high frequency radiation. These systems receive a plurality of signals, comprising the radiation that is reflected off a plurality of scatters located in the broad beam of the transmitted beam, using a receiving antenna or antennas that is/are sensitive to radiation from particular directions more than others. These broad beam radar systems can include a mechanically driven antenna to execute a predetermined scan pattern that covers a predetermined volume of space. The sensitivity of these systems is low due to the broad beam transmission. These systems are also adversely affected by the fact that radiation is received from outside the narrowly defined directions defined by the receiving antennas. These broad beam radar systems, when used as a weather radar, also collect data that is indicative of only the radial component of the wind field present in the predetermined volume of space.
One alternative in the field of monostatic radar systems are the xe2x80x9cstandardxe2x80x9d rapid-scan technology radar systems that use phased-array antennas. In these radar systems, an array of emitters are used to sequentially focus a narrow beam of high frequency radiation in a certain direction, then the radar system receives the backscattered radiation from that direction. The emitters are then focused in a second direction, and the radar system receives the backscattered radiation from the second direction. This process is executed seriatim to cover a predetermined volume of space. In such a system, there is no simultaneous transmission of the plurality of beams of high frequency radiation or simultaneous reception of the backscattered radiation from the plurality of beams of high frequency radiation. The operation of this radar system is a sequential process, but the radar system has the advantage of being able to quickly focus in any direction, since the focus operation is accomplished electronically, rather than mechanically as in other scanning radar systems.
One example of such a multiple beam radar system is disclosed in the series of U.S. Pat. Nos. 5,130,712, 5,175,551, 5,262,782, 5,359,330, 5,394,155, 5,442,359, 5,451,961 which disclose a stacked beam radar system for detecting microbursts in a predetermined region of space. The system uses a stacked beam antenna and a single pulse radar transmitter to output a pulse of radio frequency energy at a predetermined frequency. The system then uses a beam selector to interconnect a one of the plurality of elevationally stacked antenna beams to a coherent receiver. The beams are sequentially selected to provide a continuous elevation sector coverage and the antenna is then mechanically rotated in the azimuth direction.
An alternative to monostatic radar systems are the bistatic radar systems which use a single radar transmitter and a plurality of passive, low-gain receivers, at least one of which is located remotely from the transmitter site, such as is disclosed in U.S. Pat. No. 5,410,314, U.S. Pat. No. 5,469,169, U.S. Pat. No. 5,471,211. In such a system, the transmitter produces a xe2x80x9cpencil beamxe2x80x9d of high frequency energy, which is reflected off scatterers as the rotating antenna scans the predetermined volume of space. The reflected radial component of the beam is received by a receiver located at the transmitter site, while other components of the reflected beam are received at other receivers located remote from the transmitter site. The bistatic radar system has the advantage of receiving backscattered reflections indicative of the radial component of the scatterer as well as other components, which enable the system to simply produce a three-dimensional determination of the characteristics of the scatterers. This radar system is relatively inexpensive due to the use of the plurality of passive, low-gain receivers, but does require the use of an expensive mechanically driven antenna to execute a predetermined scan pattern that covers a predetermined volume of space. Furthermore, the system is limited in its ability to revisit particular locations in space since the transmitting antenna produces a single beam and is mechanically moved.
Thus, existing monostatic and bistatic radar systems are relatively expensive to implement, rely on a complex mechanically driven antenna to execute a predetermined scan pattern that covers a predetermined volume of space, and suffer from a low data refresh rate which limits the accuracy of the data that is produced.
The above described problems are solved and a technical advance achieved in the field by the present multiple beam radar system, which uses multiple simultaneously transmitted beams of high frequency energy to identify scatterers that are located in a predetermined volume of space. This multiple beam radar system simultaneously transmits several beams of high frequency energy, produced by an antenna which operates in a mechanically scanning mode, and simultaneously receives the returned radiation, which constitutes components of this narrow beam that have been reflected off scatterers located in the path of the beam. The transmitted (and thus received) frequency of each beam is different, providing information relating to the presence, locus and characteristics of the scatterers by analyzing the plurality of received beams. Each of the simultaneously transmitted beams are focused in a different direction by virtue of the fact that the antenna transmits beams of different frequencies in different directions, with the direction of each beam and the separation between beams being a function of the transmitted frequencies and the characteristics of the antenna.
The present multiple beam radar system is much less expensive to implement than phased-array systems. This is because the multiple beams are produced by simultaneously transmitting different frequencies and because the beam scanning is conducted mechanically in one axis, typically an azimuthal direction. Contamination of signals from energy received from directions outside the received beams is reduced by virtue of the use of high gain (pencil-beam) transmit and receive beam patterns.